The present invention comprises an improvement over the apparatus described in the above-identified issued U.S. patent. Set forth below is a basic description of the probe as described in the issued patent which is provided to facilitate a better understanding of the improvement of the current invention. Referring now to FIGS. 1 and 2, there is shown an embodiment of a probe 10 for detecting and measuring particulates suspended in molten metal.
The probe 10 is generally elongated and cylindrical and includes an insertion end 12 and a connector end 14. The probe connector end 14 is adapted to be secured to a supporting structure (not shown) of type well known to those of ordinary skill in the art and employed for inserting measuring probes into molten metal. The probe 10 comprises an elongated closed end inner tube 16, made of an electrically insulative material, such as quartz, which is capable of withstanding the high temperatures present in a bath of molten steel or other molten metal. The insertion end of the inner tube 16 is closed and the connector end is sealed by a suitable generally cylindrical, electrically insulative plug or seal member 18, which is preferably made of a polymeric material and is secured within the open end of the inner tube 16 utilizing a suitable adhesive 20 to form a gas tight seal. The insertion end of the inner tube 16 forms a molten metal receiving chamber 15. At least one orifice 17 extends through the inner tube 16 proximate to the insertion end to permit molten metal to flow into the molten metal receiving chamber 15 when the probe 10 is inserted into molten metal.
A gas passageway 22 comprised of a generally cylindrical, generally tubular member, extends through the seal member 18 and into at least a portion of the inner tube 16. The gas passageway 22 is preferably formed of an electrically conductive metal, such as steel. At least one and preferably a pair of elongated generally cylindrical members or wires 24 are securely connected (mechanically and electrically) to the gas passageway 22 (preferably by welding, brazing or soldering) and extend along the interior of the inner tube 16, terminating proximate to the insertion end of the inner tube 16. The elongated cylindrical members 24 are formed of an electrically conductive material and, in combination with the gas passageway 22 establish a first electrode extending into the molten metal receiving chamber 15. The inner tube 16 is surrounded by a generally tubular, electrically conductive member 26. The inner dimension of the tubular member 26 is at least slightly greater than the outer dimension of the inner tube 16 so that a small annular space 28 separates the tubular member 26 from the outer surface of the inner tube 16. The tubular member 26 establishes a second electrode outside of the inner tube 16. A spacer 34 is inserted between the insertion end of the tubular member 26 and the inner tube 16 to maintain the annular space 28 and to prevent the insertion end of the inner tube 16 from wobbling and to help prevent breakage of the inner tube 16 during shipping and handling. At least a substantial portion of the tubular member 26 is surrounded by an outer sheath 30 formed of a heat resistant material to provide thermal insulation to the tubular member 26 when the probe 10 is inserted into molten metal.
As best shown in FIG. 2, a portion of the tubular member 26 extends beyond the outer sheath 30, such that when the probe 10 is inserted into molten metal, the tubular member 26 is exposed directly to the molten metal. The insertion end of the inner tube 16 is initially covered by a metal slag cap 36 and a paper cap 38 to protect the inner tube 16 and particularly, the orifice 17 from contamination as the probe 10 is inserted through the slag layer that typically covers molten metals during processing.
In use, the connector end 14 of the probe 10 is adapted to be temporarily connected to a suitable supporting structure (not shown). A valve 42 is connected to a vacuum source 44 and a purge gas source 46. When the valve 42 is in a first position, the vacuum source 44 is in fluid communication with the inner tube 16 through the gas passageway 22 to thereby create a vacuum within the molten metal receiving chamber 15. The creation of a vacuum within the chamber 15 facilitates the flow of molten metal through the orifice 17 and into the chamber 15. When the valve 42 is in a second position, gas from the purge gas source 46 is supplied through the gas passageway 22 to the interior of the inner tube 16 to preclude the flow of molten metal or contaminates through the orifice 17 and into the chamber 15.
When the probe 10 is connected to the supporting structure direct electrical connections are established between the connector end of the gas passageway 22 (first electrode) and the connector end of the tubular member 26 (second electrode) and an external measurement device 48. The measurement device 48 is of a type well known to those of ordinary skill in the art for using the electric sensing zone method to detect and measure particulates suspended in molten metal. When the probe 10 is inserted into molten metal, the measurement device 48 establishes a current path between the first and second electrodes and passing through the orifice 17 for measuring changes in the electrical potential between the first and second electrodes which are produced by the passage of particulates entrained in the molten metal passing through the orifice 17.
A liquidus depressing material 50 is provided within the insertion end of the inner tube 16, proximate to the orifice 17. The liquidus depressing material 50 alloys with the molten metal entering the chamber 15 through the orifice 17 and the resulting alloy has a liquidus temperature which is lower than the liquidus temperature of the molten metal entering the chamber 15. Because the wires 24 are close to the wall of the inner tube 16 the cooling of the liquid metal in the central up-welled area is prevented.
In use, the probe 10 is secured to the supporting structure (not shown), so that the first and second electrodes are electrically connected to the measurement device 48 and so that the gas passageway 22 is in fluid communication with the valve 42. Initially, the valve 42 is in the second position, so that an inert purge gas from the purge gas source 46 flows through the gas passageway 22, into the inner tube 16 and out of the orifice 17.
As the probe 10 is inserted through an upper slag layer and into the molten metal, the paper cap 38 is destroyed and the metal slag cap 36 melts to expose the insertion end of the inner tube 16 and the tubular member 26 to the molten metal. As the molten metal engages the inner tube 16, the orifice 17 is effectively sealed causing an increase in gas pressure of the purge gas which is measured by external instrument (not shown). At this time, the valve 42 is changed to the first position, so that the vacuum source 44 is in fluid communication with the gas passageway 22 and the interior of the inner tube 16 to effectively create a vacuum within the chamber 15, thereby causing the molten metal to flow through the orifice 17 and into the chamber 15. As soon as the molten metal engages the wires 24, a complete electrical circuit is established and the measurement device 48 causes current to flow between the electrodes and passing through the orifice 17 for measuring changes in the electrical potential between the electrodes produced by the passage of particulates entrained in the molten metal as they pass through the orifice 17.
The detection and measuring process continues until the chamber 15 is filled with liquid metal and the level of the liquid metal effectively blocks the insertion end of the gas passageway 22 to preclude further vacuum pressure in the chamber 15. The blocking method effectively limits more sample material from entering chamber 15 and thus provides a means for creating a predetermined fixed volume of sampled metal without adding additional heat absorbing components.